1. Field of the Invention
The invention involves to the technology of optical molecular imaging modality-Bioluminescence tomography (BLT), especially involving an adaptive-finite-element-based multi-spectral reconstruction.
2. Description of the Related Art
As a new optical molecular imaging modality, BLT has rapid development and extensive application. Because the current technique can only produce a two-dimensional image, researchers can not readily detect a variety of regions of interest, which would be detectable by the development of BLT. Bioluminescence tomography is ill-posed, which means that BLT solution generally is not unique. It is necessary to incorporate a priori information for accurate BLT reconstruction, and how to make reasonable use of a priori information need to be further considered.
With the development of BLT, kinds of a priori information have been used to reconstruct the source, such as the surface light intensity distribution, the internal anatomic structure of reconstruction region, the optical properties distribution, the spectral characteristics and the physical meaning of the bioluminescent light source. All of these severely affect the reconstructive results of the light source. Generally, existing reconstruction algorithm can be divided into two categories: one is based on a priori permissible source region; the other is based on multi-spectral. Through the combination of the surface light intensity distribution and the internal anatomic structure of reconstruction region, the region of source can be generally inferred, thus a better permissible source region less than the overall region can be obtained as initial region to solve the uniqueness problem of the reconstruction. The broad spectrum characteristics of bioluminescent light source are often used. Because materials in different optical spectra have different absorption and scatter coefficients, the detection of different spectra helps to accurately locate the source. It is worth mentioning that the relevant scientific literature expatiates that if only the multi-spectral information is considered and a heterogeneous reconstruction target is regarded as a homogeneous reconstruction target, the light source reconstruction, especially for a deep light source, is not sufficient.
The BLT considers the whole object as the reconstruction region, which will increase the computational burden, and also make it difficult to restrict the permissible results. In addition, with the introduction of multi-spectral and the development of the non-contact detection mode, the large-scale data set seriously affects source reconstruction speed. In the field of optical molecular imaging, although the analytical methods, which shall be able to significantly improve the computational speed, are well developed, it is not suitable to solve the region with complex inner structure. The numerical approaches are widely developed and used as flexible reconstruction methods, and some acceleration algorithms are also further studied, for example, the multi-mesh method. However, the multi-mesh method needs to uniformly refine the mesh of the whole region, which will not only result in great computational burden for BLT but is also unnecessary.
Finite element method is widely used in bioluminescence tomography. In view of the finite element analysis, the quality of BLT reconstruction is not only related to the signal-noise-ratio (SNR) of measured data but also to the discretization of the domain. To a large extent, the finer the discretized mesh becomes, the better the reconstruction is. However, the overly detailed mesh may aggravate the ill-posedness of the BLT problem and increase the numerical instability and computational cost. Compared with general finite element method, multi-spectral measurements, and anatomical and optical information first deal with the non-uniqueness of BLT and constrain the possible solution of source reconstruction in adaptive finite element multi-spectral reconstruction method. The use of adaptive mesh refinement and permissible source region based on a posteriori measures not only avoids the dimension disaster arising from the multi-spectral measured data but also reduces the ill-posedness of BLT and therefore improves the reconstruction quality.